1. Field of the Invention
The present invention relates to a system for forming images on the sheets and outputting the sheet whereon the images are formed, more particularly, to an insert sheet transporting apparatus, an insert sheet transporting method and an image forming apparatus for transporting, loading the sheets from a plurality of sheet feeding stages and preparing the bundles of the sheets that the sheets supplied from a plurality of sheet feeding stages are mixed.
2. Description of the Related Art
The conventional image forming apparatus, such as the copying machine, is designed for being capable of operating in the modes such as the cover placing mode, the insert sheet mode of the like. These modes are designed and controlled for permitting the sheets supplied from the cassette or the sheet feeding tray provided with the image forming apparatus to be placed on the first page and after the last page or inserted between pages. Therefore, even the sheets supplied from sheet feeding stage other than that of the present bundle of the sheets can be added as “a front cover” or “a back cover” or inserted as “an insert sheet”. Further, in the similar fashion, the sheet supplied from a special tray for loading “the insert sheets” can also be inserted. In such a system, the insert sheet is required to undergo a mere transport process, so that the order of insertion (place of insertion), the number of sheet to be inserted can be set freely. Thus, the bundle of the sheets including the inserted sheets can undergo the post-processing such as the processing as a bundle of the sheets, i.e., the discharge in the form of a bundle, processing for binding, processing for folding, processing for bookbinding by the finisher or the like, which is provided with the main unit of the image forming apparatus.
Hereinafter, the operation modes, which insert the sheets supplied from the insert sheet stage as the “front cover”, “insert sheet” and “back cover”, are generally called “the insert sheet mode.”
In the method for supplying the insert sheet from the cassette, when the timing for the insertion of the sheet comes, the insert sheet is fed into the transport pass of the sheet whereon the image is to be formed, and the fed insert sheet is discharged by way of the transport pass. In this system, a fixing stage is provided on the course of the previously mentioned transport path, and the insert sheet passes the fixing stage similarly to the non-fixed sheet.
Where the original having the color image printed thereon is fed as the insert sheet, there happens sometimes that the quality of the printed image is damaged due to the effect of the heat and pressure while the insert sheet passes the fixing stage. Further, as the personal computers spread the use of the color images has also increased, thereby causing the increase in the use of the color copied papers/color printed papers as the insert sheets. When such color copied papers are supplied from the cassette, the transport efficiency of such color copy papers tends to fall due to the influence of the oil or the like deposited on the surfaces thereof, sometimes causing a marked fall of the reliability of the non-fixed sheet transport operation.
Further, there has been developed an apparatus comprising the finisher provided with the sheet feeder for supplying the insert sheets so that the insert sheets can be supplied from the finisher. As the examples of this type of apparatus, there are those published under Japanese Patent Application Laid-open Nos. 60-180894(1985), 60-191932(1985), 60-204564(1985) and the like. More particularly, in the cases of those apparatuses recited in said publications, the insert sheets are supplied to the finisher from the insert sheet feeder at predetermined time and transported to and stored in the intermediate tray of the finisher in the loaded state. The printed sheets discharged from the main unit of the image forming apparatus are also guided into the finisher and transported to the intermediate tray for being loaded thereon. In order to let the apparatus perform such an operation, it is necessary for the printed sheets to have supplied in the number required, arranged in the order corresponding to the contents of the images and loaded in advance on the storage device of the insert sheet feeder.
When selecting the sheet insert mode in combination with the insert sheet feeder, it is necessary for the insert sheets supplied from the insert sheet feeder to be fed individually and accurately into the finisher. In this stage, since the insert sheets are to be used in a variety of quality and for a variety of images, when the insert sheets undergo the automatic separation/transport stage, the stability in operation tend to differ from that in the case of the blank sheets for recording. For instance, it gives rise to a problem such that two insert sheets in overlapped condition are fed from the insert sheet feeder causing the so-called “overlapped transport”, which put the sequence of the sheets in subsequent bundle out of order.
In a conventional image forming apparatus, the necessary number of sheets to be outputted is set by the operating section thereof, and the image forming operation is continued until coming to an end thereof; in such an apparatus, when the overlapped transport of the insert sheets has occurred, the insert sheets will be inserted at wrong places in all bundles of the sheets after the point at which the overlapped transport has occurred, thereby causing the disadvantages such as the wastes of paper, time, power and the like.
Further, in the case of a system designed for enabling to stop its operation once to permit the examination of what has happened during the operation up to the point where the supply of sheet bundle is discontinued, it is possible for the user to detect the occurrence of the overlapped transport, if any, earlier than in the case of the system wherein the detection is made without stopping all the operations of the system. However, in the case where a bundle consists of a large number of sheets, even if the user has visually detected the overlapped transport, the operation of the system will continue until the system is stopped, so that even such a system is disadvantageous for the user, since the waste supply of the sheets still occurs.
Thus, the object of the present invention lies in providing an apparatus capable of making the recovery of its normal state without discontinuing the operation of the system, even if the overlapped transport of the insert sheets has occurred, by properly controlling the image forming apparatus and the finisher, thereby improving the utility of the image forming apparatus for the users.